Knee ligament balancer

ABSTRACT

An orthopaedic surgical device comprises a first sensor component and a second sensor component. Each sensor component includes a paddle set to contact a proximal tibia and a distal femur of a patient. The first sensor component and the second sensor component being movable with respect to one another to extend one paddle set beyond the other paddle set, and each paddle set includes cutouts for the clearance of the patellar tendon to avoid the need to evert the patella during use.

This application is a divisional of U.S. patent application Ser. No.12/147,708, filed on Jun. 27, 2008 and issued as U.S. Pat. No. 8,197,489on Jun. 12, 2012. That application is incorporated in its entiretyherein by reference.

CROSS-REFERENCE TO RELATED U.S. PATENT APPLICATION

Cross-reference is made to U.S. Utility patent application Ser. No.11/094,956 entitled “Method and Apparatus for use in Balancing Ligamentsof a Knee” by Mark R. DiSilvestro, which was filed on Mar. 31, 2005, theentirety of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to devices and methods for usein the performance of orthopaedic surgical procedures such as kneereplacement procedures.

BACKGROUND

In some orthopaedic surgical procedures, such as a total kneereplacement procedure, ligament balancing devices (commonly known asligament balancers) may be used to balance the surrounding soft tissue(i.e., ligaments) of a patient's joint. For example, in a total kneereplacement procedure, ligament balancing may be performed to ensure agenerally rectangular shaped extension gap and a generally rectangularshaped flexion gap at a predetermined joint force value between thepatient's natural or prosthetic proximal tibia and the patient's naturalor prosthetic distal femur.

To do so, a ligament balancer may be used to measure the medial andlateral joint forces and the medial and lateral gap displacements whenthe patient's leg is in extension (i.e., the patient's tibia ispositioned at about 0 degrees relative to the patient's femur) and inflexion (i.e., the patient's tibia is positioned at about 90 degreesrelative to the patient's femur). In either extension or flexion, if themedial and lateral gap displacements are not approximately equal (i.e.,do not form a generally rectangular shaped joint gap) at thepredetermined joint force value, ligament release may be performed toequalize the medial and/or lateral gap displacements.

SUMMARY

An orthopaedic surgical device may include a first sensor component anda second sensor component. The first sensor component may include afirst paddle set and the second sensor component may include a secondpaddle set. The first sensor component and the second sensor componentmay be movable with respect to one another to extend one paddle setbeyond the other paddle set.

Moreover, the posterior ends of the extended paddle set and the otherpaddle set may be inserted into a side of a patient's knee withouteverting a patella of the knee. The posterior ends of the extendedpaddle set may contact portions of a tibia and femur that lie away fromthe side into which the posterior ends of the extended paddle set wereinserted. The posterior ends of the other paddle set may contactportions of the tibia and the femur that lie toward the side into whichthe posterior ends of the paddle set were inserted.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention described herein is illustrated by way of example and notby way of limitation in the accompanying figures. For simplicity andclarity of illustration, elements illustrated in the figures are notnecessarily drawn to scale. For example, the dimensions of some elementsmay be exaggerated relative to other elements for clarity. Further,where considered appropriate, reference labels have been repeated amongthe figures to indicate corresponding or analogous elements.

FIGS. 1-4 show various perspective views of an embodiment of a ligamentbalancer.

FIGS. 5-6 show perspective views of another embodiment of a ligamentbalancer.

FIG. 7 shows a perspective view of yet another embodiment of a ligamentbalancer.

FIG. 8 shows a first sensor component interfacing with a distal femurand a proximal tibia.

DETAILED DESCRIPTION OF THE DRAWINGS

While the concepts of the present disclosure are susceptible to variousmodifications and alternative forms, specific exemplary embodimentsthereof have been shown by way of example in the drawings and willherein be described in detail. It should be understood, however, thatthere is no intent to limit the concepts of the present disclosure tothe particular forms disclosed, but on the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

References in the specification to “one embodiment”, “an embodiment”,“an example embodiment”, etc., indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to effect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

Moreover, the following description and claims use the terms “first” and“second” to succinctly and distinctly identify similar components.However, it should be appreciated that the terms “first” and “second” inthe following description and claims are used merely for convenience ofdescription and are not meant to require a sequential or orderedrelationship between such components.

Referring to FIGS. 1-5, an embodiment of a ligament balancer 10 for usein an orthopaedic surgical procedure is shown. The ligament balancer 10may include a sensor component 20 which is slideably coupled to a sensorcomponent 40 via a sliding mechanism 120 (FIG. 4). As shown in FIG. 1,the sensor component 20 may include a support 22 from which a paddle set24 extends in a general extension direction D. The paddle set 24 mayinclude a tibial paddle 26 having a posterior end 28 to contact aproximal tibia 210 (FIG. 8) and an anterior end 30 coupled to thesupport 22. The paddle set 24 may further include a femoral paddle 32having a posterior end 34 to contact a distal femur 220 (FIG. 8) and ananterior end 36 coupled to the support 22. Furthermore, as shown in FIG.4, the tibial paddle 26 may include a mounting slot or aperture 37configured to receive additional instrumentation such as a flexionadapter, a distal femoral cutting block, and/or an anterior/posteriorresection guide.

Similarly, the sensor component 40 may include a support 42 from which apaddle set 44 extends in a general extension direction D. The paddle set44 may include a tibial paddle 46 having a posterior end 48 to contact aproximal tibia 210 (FIG. 8) and an anterior end 50 coupled to thesupport 42. The paddle set 44 may further include a femoral paddle 52having a posterior end 54 to contact a distal femur 220 (FIG. 8) and ananterior end 56 coupled to the support 42. Furthermore, as shown in FIG.4, the tibial paddle 46 may include a mounting slot or aperture 57configured to receive additional instrumentation such as a flexionadapter, a distal femoral cutting block, and/or an anterior/posteriorresection guide.

As explained in more detail below, the support 22 generally defines asensor to sense a displacement between paddles 26, 32 of the paddle set24 and a tensor to sense and/or provide a force between paddles 26, 32of the paddle set 24. Similarly, the support 42 generally defines asensor to sense a displacement between paddles 46, 52 of the paddle set44 and a tensor to sense and/or provide a force between paddles 46, 52of the paddle set 44.

Moreover, the support 22 permits movement of the femoral paddle 32 withrespect to the tibial paddle 26 to determine a displacement 230 betweena portion 212 of the proximal tibia 210 and a condyle 222 of the distalfemur 220. See, FIG. 8. Likewise, the support 42 permits movement of thefemoral paddle 52 with respect to the tibial paddle 46 to determine adisplacement 232 between a portion 214 of the proximal tibia 210 and acondyle 224 of the distal femur 220. Referring to FIGS. 1 and 8, thepaddle set 24 and paddle set 44 may have patellar tendon cutouts 25, 45to permit entry of the paddle set 24 and the paddle set 44 into the kneewithout everting the patella and the patellar tendon 240 as the cutouts25, 45 provide clearance between the paddle sets 24, 44 and the patellartendon 240.

Referring now to FIGS. 1 and 3, each support 22, 42 includes a housing70 having an upper end 72 and a lower end 74, a displacement cylinder 76having an upper end 78 and a lower end 80, and a tensor cylinder 82having an upper end 84 and a lower end 86. As shown, an anterior end 30,50 of each tibial paddle 26, 46 may be coupled to a respective housing70 such that each tibial paddle 26, 46 generally extends away from thehousings 70 in the extension direction D. Further, an anterior end 36,56 of each femoral paddle 32, 52 may be coupled to a respectivedisplacement cylinder 76 such that each femoral paddle 32, 52 generallyextends away from the displacement cylinder 76 in the extensiondirection D.

The housing 70, displacement cylinder 76 and tensor cylinder 82 of eachsupport 22, 42 may be telescopically coupled to one another. To thisend, the housing 70 and each cylinder 76, 82 in one embodiment comprisesa circular cross section and a slightly different internal and externaldiameter. However, it should be appreciated that the housing 70 andcylinders 76, 82 may comprise other shapes such as, for example, square,oval, triangular or other cross sections. Each tensor cylinder 82 may betelescopically coupled with a corresponding housing 70. In particular,in one embodiment, the upper end 84 of the tensor cylinder 82 may beinserted into the lower end 74 of the housing 70 permitting movement ofthe lower end 86 of the tensor cylinder 82 in relation to the lower end74 of the housing 70 as the tensor cylinder 82 is extended from orretracted into the housing 70.

Each displacement cylinder 76 may be telescopically coupled with acorresponding tensor cylinder 82 and housing 70. In particular, in oneembodiment, the lower end 80 of a displacement cylinder 76 may beinserted into the upper end 84 of a tensor cylinder 82 permittingmovement of the upper end 78 of the displacement cylinder 76 in relationto the lower end 86 of the tensor cylinder 82 as the displacementcylinder 76 extends from or retracts into the tensor cylinder 82. Asshould be appreciated, telescopically coupling the displacement cylinder76 with the tensor cylinder 82 also telescopically couples thedisplacement cylinder 76 with the housing 70 due to the displacementcylinder 76 being telescopically coupled with the tensor cylinder 82.

Each support 22, 42 further includes a rail 90 coupled to the housing 70such that a distal end of the rail 90 extends beyond the lower end 74 ofthe housing 70. A locking mechanism 92 couples the tensor cylinder 82 tothe rail 90. In particular, the locking mechanism 92, when locked,prevents the tensor cylinder 82 from moving in relation to the housing70. When released or unlocked, the locking mechanism 92 slides along therail 90 thus permitting the tensor cylinder 82 to be moved in relationto the housing 70. More specifically, when unlocked, the tensor cylinder82 may be extended from the housing 70 thus resulting in the lower end86 of the tensor cylinder 82 being extended away from the lower end 74of the housing 70, or the tensor cylinder 82 may be retracted into thehousing 70 thus resulting in the lower end 86 of the tensor cylinder 82being retracted toward the lower end 74 of the housing 70. Furthermore,a pin or stop 93 on the rail 90 may prevent over extending the tensorcylinder 82 and/or accidentally sliding the locking mechanism 92 off therail 90.

In the embodiment shown in FIGS. 1-4, the tensor cylinder 82 includes alever 94 coupled toward the lower end 86 to aid in extending orretracting the tensor cylinder 82. Moreover, the locking mechanism 92includes a release lever 96 aligned with the lever 94 of the tensorcylinder 82. In operation, the user may squeeze the lever 94 and releaselever 96 together in order to unlock the tensor cylinder 82 and adjustthe position of the tensor cylinder 82. A leaf spring 98 of the lockingmechanism 92 may return the locking mechanism 92 to a locked state inresponse to the user releasing the lever 94 and release lever 96, thuslocking the tensor cylinder 82 into place.

Furthermore, the housing 70 includes a lever 97 coupled toward the lowerend 74 to aid in adjusting displacement between paddles of thecorresponding paddle set 24, 44. It should be appreciated that raisingthe lever 97 with respect to a locked lever 94 generally results inreducing the displacement between paddles of the corresponding paddleset 24, 44. Conversely, lowering the lever 97 with respect to the lockedlever 94 generally results in increasing the displacement betweenpaddles of the corresponding paddle set 24, 44.

In another embodiment of a ligament balancer 10′ shown in FIGS. 5-6, thetensor cylinder 82′ includes a handle 94′ coupled toward the lower end86′ of the tensor cylinder 82′ to aid in extending or retracting thetensor cylinder 82′. Moreover, the locking mechanism 92′ includes arelease lever 96′ aligned with the handle 94′ but shorter in length thanthe handle 94′ to permit use of the handle 94′ without releasing thelocking mechanism 92′. The locking mechanism 92′ further includes anextension spring 98′ coupled to the rail 90′ and the release lever 96′to return the locking mechanism 92′ to a locked state in response to theuser releasing the release lever 96′.

Furthermore, the housing 70′ includes a lever 97′ coupled toward thelower end 74′ to aid in adjusting displacement between paddles of thecorresponding paddle set 24′, 44′. It should be appreciated that raisingthe lever 97′ with respect to a locked lever 94′ generally results inreducing the displacement between paddles of the corresponding paddleset 24′, 44′. Conversely, lowering the lever 97′ with respect to thelocked lever 94′ generally results in increasing the displacementbetween paddles of the corresponding paddle set 24′, 44′.

As shown in FIG. 2, each support 22, 42 may include a compression spring100 positioned within and coaxial to the housing 70, displacementcylinder 76, and tensor cylinder 82. In particular, the spring 100 maybe positioned between the lower end 86 of the tensor cylinder 82 and theupper end 78 of the displacement cylinder 76. The spring 100 may asserta force between the lower end 86 of the tensor cylinder 82 and the upperend 78 of displacement cylinder 76. A user of the ligament balancer 10may selectably adjust the load upon the compression spring 100 byreleasing the locking mechanism 92 and extending or retracting thetensor cylinder 82 via levers 94, 96. The load upon the compressionspring 100 results in the compression spring 100 applying a force to thedisplacement cylinder 76 which translates the selectable force to thefemoral paddle 32, 52 of the corresponding paddle set 24, 44.

The housing 70 and tensor cylinder 82 respectively include openings 102,104. The housing opening 102 and tensor opening 104 are aligned suchthat an indicator 106 upon the displacement cylinder 76 may be viewedthrough the openings 102, 104. Since the tibial paddles 26, 46, in oneembodiment, are stationary with respect to the corresponding housings70, movement of the indicator 106 in relation to the housing 70corresponds to movement of the corresponding femoral paddle 32, 52 toits corresponding tibial paddle 26, 46. Accordingly, the housing 70, inone embodiment, includes a displacement scale 108 which relates theposition of the indicator 106 relative to the housing 70 to thedisplacement of the corresponding femoral paddle 32, 52 from itscorresponding tibial paddle 26, 46.

Since compression spring 100 is positioned between the lower end 86 ofthe tensor cylinder 82 and the upper end 78 of the displacement cylinder76 in one embodiment, movement of the indicator 106 in relation to thetensor cylinder 82 corresponds to the load upon the compression spring100 and the selectable force applied between paddles of thecorresponding paddle set 24, 44. Accordingly, the tensor cylinder 82, inone embodiment, includes force ranges 110 which relate the position ofthe indicator 106 relative to the tensor cylinder 82 to the forceapplied between the corresponding paddle set 24, 44. In one embodiment,the tensor cylinder 82 includes three force ranges labeled A, B and C inthe figures. However, other embodiments may include a different numberof force ranges or may include a force scale providing a measurement ofthe force applied to the corresponding paddle set 24, 44 instead of orin addition to an indication of a general range.

As mentioned above, the sensor component 20 is slideably coupled to thesensor component 40 via a sliding mechanism 120 (FIG. 4). The slidingmechanism 120 generally permits extending the posterior ends of onepaddle set 24, 44 in the extension direction D so that posterior ends ofthe extended paddle set 24, 44 extend beyond in posterior ends of theother paddle set 24, 44. As shown in FIGS. 2 and 3, the slidingmechanism 120 in one embodiment may include a track 122 and a runner124. The track 122 may be coupled to or otherwise incorporated into thetibial paddle 26. The track 122 may also run generally along the lengthof the tibial paddle 26 in the extension direction D between itsanterior end 30 and the posterior end 28. The runner 124 may be coupledto or otherwise incorporated into the tibial paddle 46 near a midpointbetween its posterior end 48 and anterior end 50. In another embodiment,the track 122 is coupled to the tibial paddle 46 and the runner 124 iscoupled to the tibial paddle 26.

The runner 124 may be slideably coupled to the track 122 therebyslideably coupling the sensor component 40 to the sensor component 20.In particular, the runner 124 may be restricted to movement along thetrack 122 in the extension direction D. Accordingly, moving the sensorcomponent 20 in the extension direction D with respect to the sensorcomponent 40 results in the runner 124 of the sliding mechanism 120following the track 122 in the extension direction D.

Referring now to FIGS. 5-6 another embodiment of the sliding mechanismis shown. The sliding mechanism 120′ of FIGS. 5-6 may include a trackand a runner similar to the track 122 (FIG. 2) and runner 124 (FIG. 3)of the balancer 10. The track may be coupled to or otherwiseincorporated into the tibial paddle 26′. The track may also extendbeyond an anterior end 30′ of the tibial paddle 26′ and may rungenerally between its extended anterior end 126′ and a point between theposterior end 28′ and the anterior end 30′ of the tibial paddle 26′. Therunner may be coupled to or otherwise incorporated into the tibialpaddle 46′ near a point near its anterior end 50′. In anotherembodiment, the track is coupled to the tibial paddle 46′ and the runneris coupled to the tibial paddle 26′.

The runner may be slideably coupled to the track thereby slideablycoupling the sensor component 40′ to the sensor component 20′. Inparticular, the runner may be restricted to movement along the track inthe extension direction D. Accordingly, moving the sensor component 20′in the extension direction D with respect to the sensor component 40′results in the runner of the sliding mechanism 120′ following the trackin the extension direction D.

In the above ligament balancers 10, 10′, movement of the femoral paddlesmay generally be performed manually as a result of actuating the lockingmechanisms 92, 92′ and levers and/or handles of the ligament balancers10, 10′. The ligament balancer 10″ shown in FIG. 7, however, replacesthe manual controls of the ligament balancers 10, 10′ with automatedmechanisms. In particular, the ligament balancer 10″ may include a forcesensor 330, a displacement sensor 332, and an actuator 334 positionedwithin a housing 70″ of each sensor component 20″, 40″. Each forcesensor 330 may be operatively coupled to the displacement cylinder 76″of its respective sensor component 20″, 40″ and may generate an outputsignal, such as a voltage signal, indicative of a magnitude of forceapplied to its respective femoral paddle 32″, 52″. In one particularembodiment, each force sensor 330 may comprise a load cell such asminiature load cell.

Each displacement sensor 332 of its respective sensor component 20″, 40″may generate an output signal indicative of respective displacement 230,232 (FIG. 8) between its respective paddle set 24″, 44″. In someembodiments, each displacement sensor 332 may comprise an electricaldevice to generate electrical output signals indicative of therespective displacements 230, 232.

Each actuator 334 may be operatively coupled to a respectivedisplacement cylinder 76″ and may extend or retract the respectivedisplacement cylinder 76″ in response to a corresponding control signal.In one particular embodiment, each actuator 334 may comprise a steppermotor. In another embodiment, each actuator 334 may comprise a linearactuator. However, each actuator 334 may also be embodied as any primemover devices operable to extend or retract the respective displacementcylinders 76″.

Each support 22″, 42″ of the ligament balancer 10″ illustrated in FIG. 7may also include a user interface 336, a controller 338, and a powersupply 340 positioned on or in the respective housing 70″. The userinterface 336 may include a display screen 342 and a number of userbuttons 344. In other embodiments, however, the display screens 342 maybe replaced with a series of light-emitting-diodes (LEDs) or acollection of visual indicators to provide simplified visual feedback tothe user of the ligament balancer 10″. Additionally, in someembodiments, the user interfaces 336 may be replaced by a remote userinterface(s) such as a user interface module that is separate from thesupports 22″, 42″. In such an embodiment, the remote user interface(s)may communicate with the controllers 338 via wired or wirelesscommunication.

Each controller 338 may comprise any type of controller including, forexample, general purpose micro-controllers, microprocessors, orapplication specific integrated circuits (ASICs). Each power supply 340may comprise any device capable of supplying power to the otherrespective components such as controllers 338. In one particularembodiment, the power supplies 340 may comprise replaceable batteries.In another embodiment, the power supplies 340 may comprise rechargeablebattery packs. In such embodiments, the ligament balancer 10″ mayinclude appropriate charging contacts to allow the recharging of thebattery packs. Although in the embodiment illustrated in FIG. 7, theligament balancer 10″ includes two user interfaces, two controllers, andtwo power supplies, it should be appreciated that in other embodimentsthe ligament balancer 10″ may include only one user interface, onecontroller, and/or one power supply. For example, the ligament balancer10″ may include a single controller positioned in one of the supports22″, 42″ and communicatively coupled to each of the force sensors 330,the displacement sensors 332, and the actuators 334. Similarly, theligament balancer 10″ may include a single user interface that iscommunicatively coupled to each of the controllers 338 (or to a singlecontroller).

In use, the ligament balancers 10, 10′, 10″ may be inserted into apatient's knee via an medial, lateral or anterior approach. Referringnow to FIG. 8, the ligament balancer 10 is shown with the sensorcomponent 20 positioned such that the paddle set 24 extends beyond thepaddle set 44 in the direction of extension D. In particular, thesurgeon may slide the sensor component 20 with respect to the sensorcomponent 40 such that the paddle set 24 extends beyond the paddle set44 in the direction of extension D, thus configuring the sensorcomponent 20 for a far side of the knee 200 that is away from theapproach and the sensor component 20 for a near side of the knee 200which is proximate the approach. It should be appreciated that FIG. 1shows a converse configuration wherein the paddle set 44 extend beyondthe paddle set 24 in the direction of extension D. Also, the sensorcomponent 40 is not shown in FIG. 8 in order to not obscure theinteraction between the sensor component 20 and the knee 200.

As shown in FIG. 8, extending the paddle set 24 beyond the paddle set 44positions the posterior end 28 of the tibial paddle 26 to contact aportion 212 of the proximal tibia 210 which is away from the approach ofthe ligament balancer 10 into the knee 200. Moreover, the posterior end34 is positioned to contact a condyle 222 of the distal femur 220 whichis away from the approach. While not shown, extending the paddle set 24beyond the paddle set 44 positions the posterior end 48 of the tibialpaddle 46 to contact a portion 214 of the proximal tibia 210 which isnear the approach or entry of the ligament balancer 10 into the knee200. Moreover, the posterior end 54 is positioned to contact a condyle224 of the distal femur 220 which is near the approach.

If the knee 200 were the right knee of a patient, then the depictedapproach would be a medial approach. In which case, the portion 212 ofthe proximal tibia 210 corresponds to a lateral portion of the proximaltibia, the portion 214 of the proximal tibia 210 corresponds to a medialportion of the proximal tibia 210, the condyle 222 corresponds to alateral condyle of the distal femur 220, and the condyle 224 correspondsto a medial condyle of the distal femur 220. In such a configuration,the sensor component 20 may be referred to as a lateral sensor componenthaving a lateral paddle set to measure a lateral displacement and forcebetween lateral portions of the proximal tibia 210 and distal femur 220.Likewise, the sensor component 40 may be referred to as a medial sensorcomponent having a medial paddle set to measure a medial displacementand force between medial portions of the proximal tibia 210 and thedistal femur 220.

It should be appreciated that sliding the sensor component 20 withrespect to the sensor component 40 such that the paddle set 24 extendsbeyond the paddle set 44 in the direction of extension D as mentionedabove, would also configure the ligament balancer 10 for a lateralapproach of a patient's left knee. In which case, the portion 212 of theproximal tibia 210 corresponds to a medial portion of the proximal tibia210, the portion 214 of the proximal tibia 210 corresponds to a lateralportion of the proximal tibia 210, the condyle 222 corresponds to amedial condyle of the distal femur 220, and the condyle 224 correspondsto a lateral condyle of the distal femur 220. In such a configuration,the sensor component 20 may be referred to as a medial sensor componenthaving a medial paddle set to measure a medial displacement and forcebetween medial portions of the proximal tibia 210 and distal femur 220.Likewise, the sensor component 40 may be referred to as a lateral sensorcomponent having a lateral paddle set to measure a lateral displacementand force between lateral portions of the proximal tibia 210 and thedistal femur 220.

While the disclosure has been illustrated and described in detail in thedrawings and foregoing description, such an illustration and descriptionis to be considered as exemplary and not restrictive in character, itbeing understood that only illustrative embodiments have been shown anddescribed and that all changes and modifications that come within thespirit of the disclosure are desired to be protected.

What is claimed is:
 1. A method for balancing a knee, comprising:extending posterior ends of a first paddle set beyond posterior ends ofa second paddle set along a general direction of extension, the firstpaddle set and the second paddle set being connected and slidable alongthe general direction of extension, inserting the posterior ends of thefirst paddle set and the second paddle set into a side of the kneewithout everting a patella of the knee, contacting, with the posteriorends of the first paddle set, portions of a proximal tibia and a distalfemur that lie away from the side of the knee into which the posteriorends of the first paddle set were inserted, and contacting, with theposterior ends of the second paddle set, portions of the proximal tibiaand the distal femur that lie toward the side of the knee into which theposterior ends of the second paddle set were inserted.
 2. The method ofclaim 1, wherein extending posterior ends of a first paddle set includessliding the first paddle set with respect to the second paddle set inthe general direction of extension.
 3. The method of claim 1, whereininserting the posterior ends of the first paddle set and the secondpaddle set into a side of the knee includes inserting the posterior endsof the first paddle set and the second paddle set into a medial side ofthe knee.
 4. The method of claim 3, wherein: contacting, with theposterior ends of the first paddle set, portions of a proximal tibia anda distal femur that lie away from the side of the knee into which theposterior ends of the first paddle set were inserted includes contactinga portion of the proximal tibia and a portion of the distal femur thatlie toward a lateral side of the knee, and contacting, with theposterior ends of the second paddle set, portions of the proximal tibiaand the distal femur that lie toward the side of the knee into which theposterior ends of the second paddle set were inserted includescontacting a portion of the proximal tibia and a portion of the distalfemur that lie toward the medial side of the knee.
 5. The method ofclaim 1, wherein inserting the posterior ends of the first paddle setand the second paddle set into a side of the knee includes inserting theposterior ends of the first paddle set and the second paddle set into alateral side of the knee.
 6. The method of claim 5, wherein: contacting,with the posterior ends of the first paddle set, portions of a proximaltibia and a distal femur that lie away from the side of the knee intowhich the posterior ends of the first paddle set were inserted includescontacting a portion of the proximal tibia and a portion of the distalfemur that lie toward a medial side of the knee, and contacting, withthe posterior ends of the second paddle set, portions of the proximaltibia and the distal femur that lie toward the side of the knee intowhich the posterior ends of the second paddle set were inserted includescontacting a portion of the proximal tibia and a portion of the distalfemur that lie toward the lateral side of the knee.
 7. The method ofclaim 1, further comprising: measuring a first displacement betweenportions of the proximal tibia and the distal femur using the firstpaddle set, and measuring a second displacement between portions of theproximal tibia and the distal femur using the second paddle set.
 8. Themethod of claim 1, further comprising: selecting a first force, applyingthe first force between portions of the proximal tibia and the distalfemur using the first paddle set, selecting a second force, and applyingthe second force between portions of the proximal tibia and the distalfemur using the second paddle set.
 9. The method of claim 8, wherein:the first force is dependent upon a displacement between an upper end ofa first displacement cylinder and a lower end of a first tensorcylinder, and the second force is dependent upon a displacement betweenan upper end of a second displacement cylinder and a lower end of asecond tensor cylinder.
 10. The method of claim 9, wherein: selectingthe first force includes moving the first tensor cylinder in relation tothe first displacement cylinder, and selecting the second force includesmoving the second tensor cylinder in relation to the second displacementcylinder.
 11. The method of claim 10, wherein: moving the first tensorcylinder includes unlocking the first tensor cylinder, and moving thesecond tensor cylinder includes unlocking the second tensor cylinder.12. The method of claim 8, further comprising: outputting an indicationof the first force to a user interface, and outputting an indication ofthe second force to a user interface.
 13. The method of claim 12,wherein: the indication of the first force includes a first range offorces in which the first force lies, and the indication of the secondforce includes a second range of forces in which the second force lies.14. The method of claim 13, wherein: the first range of forces isselected from a plurality of force ranges, and the second range offorces is selected from the plurality of force ranges.
 15. The method ofclaim 8, further comprising: measuring a first displacement betweenportions of the proximal tibia and the distal femur using the firstpaddle set while applying the first force between portions of theproximal tibia and the distal femur, and measuring a second displacementbetween portions of the proximal tibia and the distal femur using thesecond paddle set while applying the second force between portions ofthe proximal tibia and the distal femur.
 16. A method for balancing aknee, comprising: extending posterior ends of a first paddle set beyondposterior ends of a second paddle set along a general direction ofextension, the first paddle set and the second paddle set beingconnected and slidable along the general direction of extension,inserting the posterior ends of the first paddle set and the secondpaddle set into a medial side of the knee without everting a patella ofthe knee, contacting, with the posterior ends of the first paddle set,portions of a proximal tibia and a distal femur that lie away from themedial side of the knee, and contacting, with the posterior ends of thesecond paddle set, portions of the proximal tibia and the distal femurthat lie toward the medial side of the knee.
 17. The method of claim 16,further comprising: selecting a first force, applying the first forcebetween portions of the proximal tibia and the distal femur using thefirst paddle set, measuring a first displacement between portions of theproximal tibia and the distal femur using the first paddle set whileapplying the first force, selecting a second force, applying the secondforce between portions of the proximal tibia and the distal femur usingthe second paddle set, and measuring a second displacement betweenportions of the proximal tibia and the distal femur using the secondpaddle set while applying the second force.
 18. A method for balancing aknee, comprising: extending posterior ends of a first paddle set beyondposterior ends of a second paddle set along a general direction ofextension, the first paddle set and the second paddle set beingconnected and slidable along the general direction of extension,inserting the posterior ends of the first paddle set and the secondpaddle set into a lateral side of the knee without everting a patella ofthe knee, contacting, with the posterior ends of the first paddle set,portions of a proximal tibia and a distal femur that lie away from thelateral side of the knee, and contacting, with the posterior ends of thesecond paddle set, portions of the proximal tibia and the distal femurthat lie toward the lateral side of the knee.
 19. The method of claim18, further comprising: selecting a first force, applying the firstforce between portions of the proximal tibia and the distal femur usingthe first paddle set, measuring a first displacement between portions ofthe proximal tibia and the distal femur using the first paddle set whileapplying the first force, selecting a second force, applying the secondforce between portions of the proximal tibia and the distal femur usingthe second paddle set, and measuring a second displacement betweenportions of the proximal tibia and the distal femur using the secondpaddle set while applying the second force.